Triphenyl monomers suitable for microstructured optical films

ABSTRACT

Optical films are described having a polymerized microstructured surface that comprises the reaction product of a polymerizable resin composition comprising at least one polymerizable ethylenically unsaturated triphenyl monomer. Also described are certain triphenyl (meth)acrylate monomers and polymerizable resin compositions.

BACKGROUND

Certain microstructured optical products, such as described in U.S. Pat.Nos. 5,175,030 and 5,183,597, are commonly referred to as a “brightnessenhancing films”. Brightness enhancing films are utilized in manyelectronic products to increase the brightness of a backlit flat paneldisplay such as a liquid crystal display (LCD) including those used inelectroluminescent panels, laptop computer displays, word processors,desktop monitors, televisions, video cameras, as well as automotive andaviation displays.

Brightness enhancing films desirably exhibit specific optical andphysical properties including the index of refraction of a brightnessenhancing film that is related to the brightness gain (i.e. “gain”)produced. Improved brightness can allow the electronic product tooperate more efficiently by using less power to light the display,thereby reducing the power consumption, placing a lower heat load on itscomponents, and extending the lifetime of the product.

Brightness enhancing films have been prepared from high index ofrefraction monomers that are cured or polymerized. Halogenated (e.g.brominated) monomers or oligomers are often employed to attainrefractive indices of for example 1.56 or greater. Another way to attainhigh refractive index compositions is to employ a polymerizablecomposition that comprises high refractive index nanoparticles such asdescribed in U.S. Publication Nos. 2006/0204745, 2006/0210726,2006/0204676, and US 2006/0128853.

SUMMARY

In one embodiment, optical films and polymerizable resin compositionsare described comprising up to 50 wt-% of one or more triphenyl(meth)acrylate monomers; and 25 wt-% to 75 wt-% of one or moredi(meth)acrylate monomers or oligomers selected from bisphenol A(meth)acrylates, aromatic epoxy (meth)acrylate, and mixtures thereof.

In other embodiments, optical films are described comprising apolymerized microstructured surface wherein the microstructured surfacecomprises the reaction product of a polymerizable resin compositioncomprising at least one triphenyl monomer having the general structure

wherein R2 is independently H, methyl, or a substituent comprising a(meth)acrylate group and at least one R2 is a substituent comprising a(meth)acrylate group;X is independently halogen, aryl, or a C₂ to C₁₂ alkyl group;R3 is independently hydrogen, methyl, aryl, or a C₂ to C₁₂ alkyl group;and and p is 0 to 5.

In another embodiment, an optical film is described comprising apolymerized microstructured surface wherein the polymerizedmicrostructured surface comprises the reaction product of apolymerizable resin composition comprising at least one polymerizablemultifunctional ethylenically unsaturated triphenyl monomer.

In yet another embodiment, a triphenyl monomer is described having thegeneral structure

wherein X is independently halogen, aryl, or a C₂ to C₁₂ alkyl group;p is 0 to 5; andR2 is independently H or a substituent comprising a (meth)acrylate groupand at least one R2 comprises a substituent comprising a (meth)acrylategroup selected from

andwherein Q is O or S;L is a C₂ to C₆ alkylene group optionally substituted with a one or morehydroxyl groups; n ranges from 1 to 10; and

R1 is H or CH₃. DETAILED DESCRIPTION

Presently described are optical films, polymerizable resin compositions,and certain triphenyl (meth)acrylate monomers. The optical filmspreferably have a polymerized microstructured surface that comprises thereaction product of a polymerizable resin composition comprising atleast one polymerizable ethylenically unsaturated triphenyl monomer.

The polymerized microstructure can be an optical element or opticalproduct constructed of a base layer and a polymerized microstructuredoptical layer. The base layer and optical layer can be formed from thesame or different polymeric material. One preferred optical film havinga polymerized microstructured surface is a brightness enhancing film.

Brightness enhancing films generally enhance on-axis luminance (referredherein as “brightness”) of a lighting device. Brightness enhancing filmscan be light transmissible, microstructured films. The microstructuredtopography can be a plurality of prisms on the film surface such thatthe films can be used to redirect light through reflection andrefraction. The height of the prisms typically ranges from about 1 toabout 75 microns. When used in an optical display such as that found inlaptop computers, watches, etc., the microstructured optical film canincrease brightness of an optical display by limiting light escapingfrom the display to within a pair of planes disposed at desired anglesfrom a normal axis running through the optical display. As a result,light that would exit the display outside of the allowable range isreflected back into the display where a portion of it can be “recycled”and returned back to the microstructured film at an angle that allows itto escape from the display. The recycling is useful because it canreduce power consumption needed to provide a display with a desiredlevel of brightness.

The brightness enhancing film of the invention generally comprises a(e.g. preformed polymeric film) base layer and an optical layer. Theoptical layer comprises a linear array of regular right prisms. Eachprism has a first facet and a second facet. The prisms are formed onbase that has a first surface on which the prisms are formed and asecond surface that is substantially flat or planar and opposite firstsurface. By right prisms it is meant that the apex angle is typicallyabout 90°. However, this angle can range from 70° to 120° and may rangefrom 80° to 100°. These apexes can be sharp, rounded or flattened ortruncated. For example, the ridges can be rounded to a radius in a rangeof 4 to 7 to 15 micrometers. The spacing between prism peaks (or pitch)can be 5 to 300 microns. For thin brightness enhancing films, the pitchis preferably 10 to 36 microns, and more preferably 18 to 24 microns.This corresponds to prism heights of preferably about 5 to 18 microns,and more preferably about 9 to 12 microns. The prism facets need not beidentical, and the prisms may be tilted with respect to each other. Therelationship between the total thickness of the optical article, and theheight of the prisms, may vary. However, it is typically desirable touse relatively thinner optical layers with well-defined prism facets.For thin brightness enhancing films on substrates with thicknesses closeto 1 mil (20-35 microns), a typical ratio of prism height to totalthickness is generally between 0.2 and 0.4.

As described in Lu et al., U.S. Pat. No. 5,175,030, and Lu, U.S. Pat.No. 5,183,597, a microstructure-bearing article (e.g. brightnessenhancing film) can be prepared by a method including the steps of (a)preparing a polymerizable composition; (b) depositing the polymerizablecomposition onto a master negative microstructured molding surface in anamount barely sufficient to fill the cavities of the master; (c) fillingthe cavities by moving a bead of the polymerizable composition between apreformed base (such as a PET film) and the master, at least one ofwhich is flexible; and (d) curing the composition. The master can bemetallic, such as nickel, nickel-plated copper or brass, or can be athermoplastic material that is stable under the polymerizationconditions, and that preferably has a surface energy that allows cleanremoval of the polymerized material from the master. One or more thesurfaces of the base film can optionally be primed or otherwise betreated to promote adhesion of the optical layer to the base.

In some embodiments, the polymerizable resin composition comprisessurface modified inorganic nanoparticles. In such embodiments,“polymerizable composition” refers to the total composition, i.e. theorganic component and surface modified inorganic nanoparticles. The“organic component” refers to all of the components of the compositionexcept for the surface modified inorganic nanoparticles. Since thesurface treatments are generally adsorbed or otherwise attached to thesurface of the inorganic nanoparticles, the surface treatments are notconsidered a portion of the organic component. When the composition isfree of inorganic materials such as surface modified inorganicnanoparticles the polymerizable resin composition and organic componentare one in the same.

The organic component as well as the polymerizable composition ispreferably substantially solvent free. “Substantially solvent free”refer to the polymerizable composition having less than 5 wt-%, 4 wt-%,3 wt-%, 2 wt-%, 1 wt-% and 0.5 wt-% of non-polymerizable (e.g. organic)solvent. The concentration of solvent can be determined by knownmethods, such as gas chromatography (as described in ASTM D5403).Solvent concentrations of less than 0.5 wt-% are preferred.

The components of the organic component are preferably chosen such thatthe polymerizable resin composition has a low viscosity. In someembodiments, the viscosity of the organic component is less than 1000cps and typically less than 900 cps at the coating temperature. Theviscosity of the organic component may be less than 800 cps, less than700 cps, less than 600 cps, or less than 500 cps at the coatingtemperature. As used herein, viscosity is measured (at a shear rate upto 1000 sec-1) with 25 mm parallel plates using a Dynamic StressRheometer. Further, the viscosity of the organic component is typicallyat least 10 cps, more typically at least 50 cps at the coatingtemperature.

The coating temperature typically ranges from ambient temperature, 77°F. (25° C.) to 180° F. (82° C.). The coating temperature may be lessthan 170° F. (77° C.), less than 160° F. (71° C.), less than 150° F.(66° C.), less than 140° F. (60° C.), less than 130° F. (54° C.), orless than 120° F. (49° C.). The organic component can be a solid orcomprise a solid component provided that the melting point in thepolymerizable composition is less than the coating temperature. Theorganic component is preferably a liquid at ambient temperature.

The triphenyl monomer and/or the organic component has a refractiveindex of at least 1.55, 1.56, 1.57, 1.58, 1.59, or 1.60. Thepolymerizable composition including high refractive index nanoparticlescan have a refractive index as high as 1.70. (e.g. at least 1.61, 1.62,1.63, 1.64, 1.65, 1.66, 1.67, 1.68, or 1.69) High transmittance in thevisible light spectrum is also typically preferred.

The polymerizable composition is energy curable in time scalespreferably less than five minutes (e.g. for a brightness enhancing filmhaving a 75 micron thickness). The polymerizable composition ispreferably sufficiently crosslinked to provide a glass transitiontemperature that is typically greater than 45° C. The glass transitiontemperature can be measured by methods known in the art, such asDifferential Scanning calorimetry (DSC), modulated DSC, or DynamicMechanical Analysis. The polymerizable composition can be polymerized byconventional free radical polymerization methods.

The presently described optical films are prepared from a polymerizableresin composition comprising at least one triphenyl monomer comprisingpolymerizable ethylenically unsaturated substituents. The ethylenicallyunsaturated substituents are preferably (meth)acrylate substituents.

Such monomers comprise a triphenyl core structure wherein the threephenyl groups are not fused, but joined by a bond. At least one of thephenyl groups has a substituent comprising a polymerizable(meth)acrylate or thio(meth)acrylate (e.g. end) group. In someembodiments, the triphenyl monomer is a monofunctional (meth)acrylatemonomer. Such monofunctional triphenyl monomer is preferably employed incombination with other multi- and in particular di-(meth)acrylatemonomers. In other embodiments, the triphenyl monomer is amulti-(meth)acrylate monomer wherein two or more of the aromatic ringsof the triphenyl core structure comprise (meth)acrylate orthio(meth)acrylate substituents.

In one embodiment, the triphenyl monomer has the general structure

In another embodiment, the triphenyl monomer has the general structure

In yet another embodiment, the triphenyl monomer has the generalstructure

In each of the structures T-1, T-2, and T-3, R2 is independently H,methyl, or a substituent comprising a (meth)acrylate group and at leastone R2 comprises a (meth)acrylate group; X is independently halogen,aryl, or a C₂ to C₁₂ alkyl group; and p is 0 to 5. R3 is independentlyhydrogen, methyl, aryl, or a C₂ to C₁₂ alkyl group. The alkyl group of Xor R3 may have a straight chain or may be branched.

The triphenyl monomer is preferably free of bromine andchlorine-containing substituents. In some embodiments, the triphenylmonomer is substantially free of other halogen-containing substituentsas well.

In some embodiments, p is 0 and thus the aromatic rings of the triphenylcore structure are unsubstituted, i.e. do not include any halogen oralkyl substituents.

R2 is independently H, methyl, or a substituent comprising a(meth)acrylate group and at least one R2 comprises a (meth)acrylategroup. R2 is typically independently a (meth)acrylate substituentselected from

wherein Q is O or S;L is a C₂ to C₆ alkylene group optionally substituted with a one or morehydroxyl groups;n ranges from 0 to 10;

R1 is H or CH₃; and

R3 is independently hydrogen, methyl, aryl, or a C₁ to C₁₂ alkyl groupas previously described.

Based on starting materials that are known to be commercially available,R2 is typically i) or ii) for the triphenyl monomer of structure T-1.Further, for the triphenyl monomer of the structure T-3, R2 is typicallyi) or iii).

In some embodiments, Q is preferably O. L is preferably C₂ or C₃.Further, n is preferably 0, 1, or 2 and in some embodiments preferably1.

The triphenyl (meth)acrylate monomers described herein can be preparedby synthetic methods as known by one of ordinary skill in the art. Forexample, triphenyl (meth)acrylate monomers can be prepared by thereaction of a triphenyl alcohol-group containing material with a(meth)acrylic acid or ester compound. In yet another synthesis, atriphenyl alcohol-group containing material can be reacted with anaromatic acid (e.g. para-toluene sulfonic acid) and a (meth)acrylic acidor ester compound. Alternatively, an epoxy starting material can bereacted with a (meth)acrylic acid or ester compound in the presence of acatalyst.

In some embodiments, the starting aromatic monoalcohol, diol, or triolis commercially available. In other embodiments, the starting aromaticalcohols can be synthesized.

Exemplary synthesis of acrylic acid2-(4-{1,1-bis-[4-(2-acryloyloxy-ethoxy)-phenyl]-ethyl}-phenoxy)-ethylester (“TTA-1”) and 2,6-diphenylphenoxyehyl acrylate (“TPA-1”) aredescribed in the forthcoming examples.

Other non-limiting examples of starting materials that can be usedinclude:

Various starting materials having the following general structure areknown having the R5, R6, R7 and R8 group as specified in Table 1 asfollows:

TABLE 1 R5 R6 R7 R8 S-3 *—OH *—H *—H *—H S-4

*—H *—H *—H S-5 *—H *—OH *—OH *—OH S-6 *—CH₃ *—OH *—H *—OH S-7 *—CH₃*—OH *—OH *—OH S-8

*—H *—H *—H S-9

*—H *—OH *—H S-10 *—CH₃ *—OH *—OH

Various starting materials having the following general structure areknown having the R9-R15 groups as specified in Table 2 as follows:

TABLE 2 R9 R10 R11 R12 R13 R14 R15 S- *—OH *—OH *—H *—H *—H *—H *—CH₃ 11S- *—H *—H *—CH₃ *—H *—H *—OH *—H 12 S- *—H *—H *—CH₃ *—OH *—H *—H *—H13 S- *—OH *—H *—H *—H *—H *—H *—H 14 S- 15 *—OH *—OH *—H *—H

*—H *—CH₃Another starting material is:

These starting materials are commercially available from varioussuppliers including Aldrich, TCI, and VWR.

After reaction, the polymerizable —OH or ═O group(s) of each of thestarting material are reacted to synthesize a molecule containing a(meth)acrylate containing substituent such as i), ii), or iii) asdescribed above.

Preferred species of triphenyl monomers include multi-(meth)acrylatestriphenyl monomers such as triphenyl tri(meth)acrylate monomers having arefractive index of at least 1.50, triphenyl di(meth)acrylate monomerhaving a refractive index of at least 1.55 and triphenylmono(meth)acrylate monomers having a refractive index of at least 1.55.Triphenyl monomers that are a (e.g. viscous) liquid at ambienttemperature (i.e. 25° C.) are also preferred for processing.

One preferred triphenyl monomer has the general structure

wherein X is independently halogen, aryl, or a C₂ to C₁₂ alkyl group;p is 0 to 5; andR2 is independently H or a substituent comprising a (meth)acrylate groupand at least one R2 comprises a substituent comprising a (meth)acrylategroup selected from

andwherein Q is O or S;L is a C₂ to C₆ alkylene group optionally substituted with a one or morehydroxyl groups; n ranges from 1 to 10; and

R1 is H or CH₃.

The amount of triphenyl (meth)acrylate monomer employed in thepolymerizable resin composition can vary. In some embodiments, thepolymerizable compositions may consist solely (i.e. 100%) of a singlemulti-(meth)acrylate triphenyl monomer such as a di(meth)acrylatetriphenyl monomer or a tri(meth)acrylate triphenyl monomer. In otherembodiments, the polymerizable composition may comprise a mixture of twoor more triphenyl monomers wherein at least one of the triphenyl(meth)acrylate monomers is a multi-(meth)acrylate. A smallconcentration, for example 1 wt-%, 2 wt-%, 3 wt-%, 4 wt-%, or 5 wt-% maybe substituted for a portion of a lower refractive index component(s) inorder to raise the refractive index of the polymerizable resincomposition.

In yet other embodiments, the polymerizable resin comprises up to 50wt-% of one or more triphenyl (meth)acrylate monomers; and 25 wt-% to 75wt-% of one or more di(meth)acrylate monomers or oligomers having atleast two polymerizable (meth)acrylate groups.

A variety of monomers and/or oligomers having at least two polymerizable(meth)acrylate groups may be employed.

Suitable urethane (meth)acrylates are commercially available fromSartomer under the trade designations “CN965”, “CN968”, “CN981”, “CN983”, “CN 984”, “CN972”, and “CN978”; from Cognis under the tradedesignation “Photomer 6210”, “Photomer 6217”, “Photomer 6230”, “Photomer6623”, “Photomer 6891”, and “Photomer 6892”; and from UCB under thetrade designations “Ebecryl 1290”, “Ebecryl 2001”, and “Ebecryl 4842”.

Suitable polyester (meth)acrylates and (meth)acrylated acrylic oligomersare also commercially available or can be prepared by methods know inthe art.

In some embodiments, the aromatic monomer is a bisphenoldi(meth)acrylate, i.e. the reaction product of a bisphenol A diglycidylether and acrylic acid. Although bisphenol A diglycidyl ether isgenerally more widely available, it is appreciated that other biphenoldiglycidyl ether such as bisphenol F diglycidyl ether could also beemployed. In other embodiments, the monomer is an aromatic epoxydi(meth)acrylate oligomer derived from a different starting monomer.

Regardless of the starting monomers, the polymerizable compositionpreferably comprises at least one aromatic (optionally brominated)difunctional (meth)acrylate monomer that comprises a major portionhaving the following general structure:

wherein Z is independently —C(CH₃)₂—, —CH₂—, —C(O)—, —S—, —S(O)—, or—S(O)₂—, each Q is independently O or S. L is a linking group. L mayindependently comprise a branched or linear C₂-C₆ alkylene group and nranges from 0 to 10. More preferably L is C₂ or C₃ and n is 0, 1, 2 or3. The carbon chain of the alkylene linking group may optionally besubstituted with one or more hydroxy groups. For example L may be—CH₂CH(OH)CH₂—. Typically, the linking groups are the same. R1 isindependently hydrogen or methyl.

The di(meth)acrylate monomer may be synthesized or purchased. As usedherein, major portion refers to at least 60-70 wt-% of the monomercontaining the specific structure(s) just described. It is commonlyappreciated that other reaction products are also typically present as abyproduct of the synthesis of such monomers. The di(meth)acrylatemonomer can be the reaction product of Tetrabromobisphenol A diglycidylether and acrylic acid. Such monomer may be obtained from UCBCorporation, Smyrna, GA under the trade designation “RDX-51027”. Thismaterial comprises a major portion of 2-propenoic acid,(1-methylethylidene)bis[(2,6-dibromo-4,1-phenylene)oxy(2-hydroxy-3,1-propanediyl)]ester.

Alternatively or in addition to, the organic component may comprise oneor more (meth)acrylated aromatic epoxy oligomers. Various(meth)acrylated aromatic epoxy oligomers are commercially available. Forexample, (meth)acrylated aromatic epoxy, (described as a modified epoxyacrylates), are available from Sartomer, Exton, Pa. under the tradedesignation “CN118”, and “CN115”. (Meth)acrylated aromatic epoxyoligomer, (described as an epoxy acrylate oligomer), is available fromSartomer under the trade designation “CN2204”. Further, a(meth)acrylated aromatic epoxy oligomer, (described as an epoxy novolakacrylate blended with 40% trimethylolpropane triacrylate), is availablefrom Sartomer under the trade designation “CN112C60”. One exemplaryaromatic epoxy acrylate is commercially available from Sartomer underthe trade designation “CN 120” (reported by the supplier to have arefractive index of 1.5556, a viscosity of 2150 at 65° C., and a Tg of60° C.).

In some embodiments, the aromatic epoxy acrylate is derived frombisphenol A, such as those of the structure previously described. Inother embodiments, the aromatic epoxy acrylate is derived from adifferent monomer than bisphenol A.

One exemplary bisphenol-A ethoxylated diacrylate monomer is commerciallyavailable from Sartomer under the trade designations “SR602” (reportedto have a viscosity of 610 cps at 20° C. and a Tg of 2° C.). Anotherexemplary bisphenol-A ethoxylated diacrylate monomer is as commerciallyavailable from Sartomer under the trade designation “SR601” (reported tohave a viscosity of 1080 cps at 20° C. and a Tg of 60° C.).

In yet another embodiment, one or more of the triphenyl (meth)acrylatemonomer(s) described here can be combined with one or more biphenyl(meth)acrylate monomers.

In some embodiments, the biphenyl (meth)acrylate monomer has the generalstructure

wherein each R1 is independently H or methyl;each R2 is independently Br;m ranges from 0 to 4;each Q is independently O or S;n ranges from 0 to 10;L is a C2 to C12 alkylene group optionally substituted with one or morehydroxyl groups;z is an aromatic ring; andt is independently 0 or 1.

In some aspects, Q is preferably O. Further, n is typically 0, 1 or 2. Lis typically C₂ or C₃. Alternatively, L is typically a hydroxylsubstituted C₂ or C₃. In some embodiments, z is preferably fused to thephenyl group thereby forming a binapthyl core structure.

Preferably, at least one of the -Q[L-O]n C(O)C(R1)=CH₂ groups issubstituted at the ortho or meta position. More preferably, the biphenyldi(meth)acrylate monomer comprises a sufficient amount of ortho and/ormeta (meth)acrylate substituents such that the monomer is a liquid at25° C. In some embodiments, each (meth)acrylate group containingsubstituent is bonded to an aromatic ring group at an ortho or metaposition. It is preferred that the biphenyl di(meth)acrylate monomercomprises a major amount of ortho (meth)acrylate substituents (i.e. atleast 50%, 60%, 70%, 80%, 90%, or 95% of the substituents of thebiphenyl di(meth)acrylate monomer). In some embodiments, each(meth)acrylate group containing substituent is bonded to an aromaticring group at an ortho or meta position. As the number of meta- andparticularly para-substituents increases, the viscosity of the organiccomponents can increase as well. Further, para-biphenyl di(meth)acrylatemonomers are solids at room temperature, with little solubility (i.e.less than 10%), even in phenoxyethyl acrylate and tetrahydrofurfurylacrylate.

Such biphenyl monomers are described in further detail in WO2008/112451.Other biphenyl di(meth)acrylate monomer are described in the literature.

In other embodiments, the triphenyl (meth)acrylate containingpolymerizable resin compositions optionally comprises one or moremonofunctional diluents in amounts up to about 50 wt-%. In someembodiments, the polymerizable resin composition comprises at least 5wt-%, 10 wt-% or 15 wt-% of such monofunctional diluents to improve theprocessability of the resin composition by reducing its viscosity.

Aromatic (e.g. monofunctional) (meth)acrylate monomers typicallycomprise a phenyl, cumyl, biphenyl, or naphthyl group. Preferreddiluents can have a refractive index greater than 1.50 (e.g. greaterthan 1.55. Such reactive diluents can be halogenated, non-brominated, ornon-halogenated.

Suitable monomers include phenoxyethyl (meth)acrylate;phenoxy-2-methylethyl (meth)acrylate; phenoxyethoxyethyl (meth)acrylate,3-hydroxy-2-hydroxypropyl (meth)acrylate; benzyl (meth)acrylate;phenylthio ethyl acrylate; 2-naphthylthio ethyl acrylate; 1-naphthylthioethyl acrylate; naphthyloxy ethyl acrylate; 2-naphthyloxy ethylacrylate; phenoxy 2-methylethyl acrylate; phenoxyethoxyethyl acrylate;3-phenoxy-2-hydroxy propyl acrylate; and phenyl acrylate.

Phenoxyethyl acrylate is commercially available from more than onesource including from Sartomer under the trade designation “SR339”; fromEternal Chemical Co. Ltd. under the trade designation “Etermer 210”; andfrom Toagosei Co. Ltd under the trade designation “TO-1166”. Phenylthioethyl acrylate (PTEA) is also commercially available from Cognis. Thestructure of these monomers is shown as follows:

In some embodiments, the polymerizable compositions comprise one or moremonofunctional biphenyl monomer(s).

Monofunctional biphenyl monomers comprise a terminal biphenyl group(wherein the two phenyl groups are not fused, but joined by a bond) or aterminal group comprising two aromatic groups joined by a linking group(e.g. Q). For example, when the linking group is methane, the terminalgroup is a biphenylmethane group. Alternatively, wherein the linkinggroup is —(C(CH₃)₂—, the terminal group is 4-cumyl phenyl. Themonofunctional biphenyl monomer(s) also comprise a single ethylenicallyunsaturated group that is preferably polymerizable by exposure to (e.g.UV) radiation. The monofunctional biphenyl monomer(s) preferablycomprise a single (meth)acrylate group or single thio(meth)acrylategroup. Acrylate functionality is typically preferred. In some aspects,the biphenyl group is joined directly to the ethylenically unsaturated(e.g. (meth)acrylate) group. An exemplary monomer of this type is2-phenyl-phenyl acrylate. The biphenyl mono(meth)acrylate or biphenylthio(meth)acrylate monomer may further comprise a (e.g. 1 to 5 carbon)alkyl group optionally substituted with one or more hydroxyl groups. Anexemplary species of this type is 2-phenyl-2-phenoxyethyl acrylate.

In one embodiment, a monofunctional biphenyl (meth)acrylate monomer isemployed having the general formula:

wherein R1 is H or CH₃;

X is O or S;

n ranges from 0 to 10 (e.g. n is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10); and

L is an alkylene group having 1 to 5 carbon atoms (i.e. methylene,ethylene, propylene, butylene, or pentylene), optionally substitutedwith hydroxy.

In another embodiment, the monofunctional biphenyl (meth)acrylatemonomer has the general formula:

wherein R1 is H or CH₃;

X is O or S;

Q is selected from —(C(CH₃)₂—, —CH₂, —C(O)—, —S(O)—, and —S(O)₂—;

n ranges from 0 to 10 (e.g. n is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10); and

L is an alkylene group having 1 to 5 carbon atoms (i.e. methylene,ethylene, butylene, or pentylene), optionally substituted with hydroxy.

Some specific monomers that are commercially available from Toagosei Co.Ltd. of Japan, include for example 2-phenyl-phenyl acrylate availableunder the trade designation “TO-2344”, 4-(-2-phenyl-2-propyl)phenylacrylate available under the trade designation “TO-2345”, and2-phenyl-2-phenoxyethyl acrylate, available under the trade designation“TO-1463”.

Various combinations of aromatic monofunctional (meth)acrylate monomerscan be employed. For example, a (meth)acrylate monomer comprising aphenyl group may be employed in combination with one or more(meth)acrylate monomers comprising a biphenyl group. Further, twodifferent biphenyl (meth)acrylate monofunctional monomera may beemployed.

The polymerizable resin may optionally comprise up to 35 wt-% of variousother (e.g. non-halogenated) ethylenically unsaturated monomers. Forexample, when the (e.g. prism) structures are cast and photocured upon apolycarbonate preformed polymeric film the polymerizable resincomposition may comprise one or more N,N-disubstituted (meth)acrylamidemonomers. These include N-alkylacrylamides and N,N-dialkylacrylamides,especially those containing C₁₋₄ alkyl groups. Examples areN-isopropylacrylamide, N-t-butylacrylamide, N,N-dimethylacrylamide,N,N-diethylacrylamide, N-vinyl pyrrolidone and N-vinylcaprolactam.

The polymerizable resin composition may also optionally comprise up to20 wt-% of a non-aromatic crosslinker that comprises at least three(meth)acrylate groups. Suitable crosslinking agents include for examplepentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,trimethylolpropane tri(methacrylate), dipentaerythritolpenta(meth)acrylate, dipentaerythritol hexa(meth)acrylate,trimethylolpropane ethoxylate tri(meth)acrylate, glyceryltri(meth)acrylate, pentaerythritol propoxylate tri(meth)acrylate, andditrimethylolpropane tetra(meth)acrylate. Any one or combination ofcrosslinking agents may be employed. Since methacrylate groups tend tobe less reactive than acrylate groups, the crosslinker(s) are preferablyfree of methacrylate functionality.

Various crosslinkers are commercially available. For example,pentaerythritol triacrylate (PETA) is commercially available fromSartomer Company, Exton, Pa. under the trade designation “SR444”; fromOsaka Organic Chemical Industry, Ltd. Osaka, Japan under the tradedesignation “Viscoat #300”; from Toagosei Co. Ltd., Tokyo, Japan underthe trade designation “Aronix M-305”; and from Eternal Chemical Co.,Ltd., Kaohsiung, Taiwan under the trade designation “Etermer 235”.Trimethylol propane triacrylate (TMPTA) is commercially available fromSartomer Company under the trade designations “SR351”. TMPTA is alsoavailable from Toagosei Co. Ltd. under the trade designation “AronixM-309”. Further, ethoxylated trimethylolpropane triacrylate andethoxylated pentaerythritol triacrylate are commercially available fromSartomer under the trade designations “SR454” and “SR494” respectively.

In some embodiments, it is preferred that the polymerizedmicrostructured surface of the optical film, the polymerizable resincomposition, and the triphenyl monomers are substantially free (i.e.contain less than 1 wt-%) of bromine. In other embodiments, the totalamount of bromine in combination with chlorine is less than 1 wt-%. Insome aspects, the polymerized microstructured surface or the opticalfilm, the polymerizable resin composition, and the triphenyl monomersare substantially non-halogenated (i.e. contains less than 1 wt-% totalof bromine, chlorine, fluorine and iodine).

The UV curable polymerizable compositions comprise at least onephotoinitiator. A single photoinitiator or blends thereof may beemployed in the brightness enhancement film of the invention. In generalthe photoinitiator(s) are at least partially soluble (e.g. at theprocessing temperature of the resin) and substantially colorless afterbeing polymerized. The photoinitiator may be (e.g. yellow) colored,provided that the photoinitiator is rendered substantially colorlessafter exposure to the UV light source.

Suitable photoinitiators include monoacylphosphine oxide andbisacylphosphine oxide. Commercially available mono or bisacylphosphineoxide photoinitiators include 2,4,6-trimethylbenzoybiphenylphosphineoxide, commercially available from BASF (Charlotte, N.C.) under thetrade designation “Lucirin TPO”; ethyl-2,4,6-trimethylbenzoylphenylphosphinate, also commercially available from BASF under the tradedesignation “Lucirin TPO-L”; and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide commercially availablefrom Ciba Specialty Chemicals under the trade designation “Irgacure819”. Other suitable photoinitiators include2-hydroxy-2-methyl-1-phenyl-propan-1-one, commercially available fromCiba Specialty Chemicals under the trade designation “Darocur 1173” aswell as other photoinitiators commercially available from Ciba SpecialtyChemicals under the trade designations “Darocur 4265”, “Irgacure 651”,“Irgacure 1800”, “Irgacure 369”, “Irgacure 1700”, and “Irgacure 907”.

The photoinitiator can be used at a concentration of about 0.1 to about10 weight percent. More preferably, the photoinitiator is used at aconcentration of about 0.5 to about 5 wt-%. Greater than 5 wt-% isgenerally disadvantageous in view of the tendency to cause yellowdiscoloration of the brightness enhancing film. Other photoinitiatorsand photoinitiator may also suitably be employed as may be determined byone of ordinary skill in the art.

Surfactants such as fluorosurfactants and silicone based surfactants canoptionally be included in the polymerizable composition to reducesurface tension, improve wetting, allow smoother coating and fewerdefects of the coating, etc.

The triphenyl (meth)acrylate monomers described herein are particularlyuseful in preparing non-halogenated high refractive index polymerizableorganic compositions. In some aspects the compositions are free ofinorganic nanoparticles.

In other embodiments, the polymerizable composition further comprisesinorganic nanoparticles.

Surface modified (e.g. colloidal) nanoparticles can be present in thepolymerized structure in an amount effective to enhance the durabilityand/or refractive index of the article or optical element. In someembodiments, the total amount of surface modified inorganicnanoparticles can be present in the polymerizable resin or opticalarticle in an amount of at least 10 wt-%, 20 wt-%, 30 wt-% or 40 wt-%.The concentration is typically less than to 70 wt-%, and more typicallyless than 60 wt-% in order that the polymerizable resin composition hasa suitable viscosity for use in cast and cure processes of makingmicrostructured films.

The size of such particles is chosen to avoid significant visible lightscattering. It may be desirable to employ a mixture of inorganic oxideparticle types to optimize an optical or material property and to lowertotal composition cost. The surface modified colloidal nanoparticles canbe oxide particles having a (e.g. unassociated) primary particle size orassociated particle size of greater than 1 nm, 5 nm or 10 nm. Theprimary or associated particle size is generally and less than 100 nm,75 nm, or 50 nm. Typically the primary or associated particle size isless than 40 nm, 30 nm, or 20 nm. It is preferred that the nanoparticlesare unassociated. Their measurements can be based on transmissionelectron microscopy (TEM). The nanoparticles can include metal oxidessuch as, for example, alumina, zirconia, titania, mixtures thereof, ormixed oxides thereof. Surface modified colloidal nanoparticles can besubstantially fully condensed.

Fully condensed nanoparticles (with the exception of silica) typicallyhave a degree of crystallinity (measured as isolated metal oxideparticles) greater than 55%, preferably greater than 60%, and morepreferably greater than 70%. For example, the degree of crystallinitycan range up to about 86% or greater. The degree of crystallinity can bedetermined by X-ray diffraction techniques. Condensed crystalline (e.g.zirconia) nanoparticles have a high refractive index whereas amorphousnanoparticles typically have a lower refractive index.

Zirconia and titania nanoparticles can have a particle size from 5 to 50nm, or 5 to 15 nm, or 8 nm to 12 nm. Zirconia nanoparticles can bepresent in the durable article or optical element in an amount from 10to 70 wt-%, or 30 to 60 wt-%. Zirconias for use in composition andarticles of the invention are available from Nalco Chemical Co. underthe trade designation “Nalco OOSSOO8” and from Buhler AG Uzwil,Switzerland under the trade designation “Buhler zirconia Z-WO sol”.

The zirconia particles can be prepared using hydrothermal technology asdescribed in Published U.S. Patent Application No. 2006/0148950. Thenanoparticles are surface modified. Surface modification involvesattaching surface modification agents to inorganic oxide (e.g. zirconia)particles to modify the surface characteristics. The overall objectiveof the surface modification of the inorganic particles is to provideresins with homogeneous components and preferably a low viscosity thatcan be prepared into films (e.g. using cast and cure processes) withhigh brightness.

The nanoparticles are often surface-modified to improve compatibilitywith the organic matrix material. The surface-modified nanoparticles areoften non-associated, non-agglomerated, or a combination thereof in anorganic matrix material. The resulting light management films thatcontain these surface-modified nanoparticles tend to have high opticalclarity and low haze. The addition of the high refractive indexsurface-modified nanoparticles, such as zirconia, can increase the gainof brightness enhancement film compared to films that contain onlypolymerized organic material.

The monocarboxylic acid surface treatments preferably comprise acompatibilizing group. The monocarboxylic acids may be represented bythe formula A-B where the A group is a (e.g. monocarboxylic acid) groupcapable of attaching to the surface of a (e.g. zirconia or titania)nanoparticle, and B is a compatibilizing group that comprises a varietyof different functionalities. The carboxylic acid group can be attachedto the surface by adsorption and/or formation of an ionic bond. Thecompatibilizing group B is generally chosen such that it is compatiblewith the polymerizable resin of the (e.g. brightness enhancing) opticalarticle. The compatibilizing group B can be reactive or nonreactive andcan be polar or non-polar.

Compatibilizing groups B that can impart non-polar character to thezirconia particles include, for example, linear or branched aromatic oraliphatic hydrocarbons. Representative examples of non-polar modifyingagents having carboxylic acid functionality include octanoic acid,dodecanoic acid, stearic acid, oleic acid, and combinations thereof

The compatibilizing group B may optionally be reactive such that it cancopolymerize with the organic matrix of the (e.g. brightness enhancing)optical article. For instance, free radically polymerizable groups suchas (meth)acrylate compatibilizing groups can copolymerize with(meth)acrylate functional organic monomers to generate brightnessenhancement articles with good homogeneity.

Suitable surface modifications are described in U.S. Publication No.2007/0112097 and U.S. Serial No. WO2008/121465.

The surface modified particles can be incorporated into the curable(i.e. polymerizable) resin compositions in various methods. In apreferred aspect, a solvent exchange procedure is utilized whereby theresin is added to the surface modified sol, followed by removal of thewater and co-solvent (if used) via evaporation, thus leaving theparticles dispersed in the polymerizable resin. The evaporation step canbe accomplished for example, via distillation, rotary evaporation oroven drying. In another aspect, the surface modified particles can beextracted into a water immiscible solvent followed by solvent exchange,if so desired. Alternatively, another method for incorporating thesurface modified nanoparticles in the polymerizable resin involves thedrying of the modified particles into a powder, followed by the additionof the resin material into which the particles are dispersed. The dryingstep in this method can be accomplished by conventional means suitablefor the system, such as, for example, oven drying or spray drying.

The optical layer can directly contact the base layer or be opticallyaligned to the base layer, and can be of a size, shape and thicknessallowing the optical layer to direct or concentrate the flow of light.The optical layer can have a structured or micro-structured surface thatcan have any of a number of useful patterns such as described and shownin the U.S. Pat. No. 7,074,463. The micro-structured surface can be aplurality of parallel longitudinal ridges extending along a length orwidth of the film. These ridges can be formed from a plurality of prismapexes. These apexes can be sharp, rounded or flattened or truncated.For example, the ridges can be rounded to a radius in a range of 4 to 7to 15 micrometers.

These include regular or irregular prismatic patterns, which can be anannular prismatic pattern, a cube-corner pattern or any other lenticularmicrostructure. A useful microstructure is a regular prismatic patternthat can act as a totally internal reflecting film for use as abrightness enhancement film. Another useful microstructure is acorner-cube prismatic pattern that can act as a retro-reflecting film orelement for use as reflecting film. Another useful microstructure is aprismatic pattern that can act as an optical element for use in anoptical display. Another useful microstructure is a prismatic patternthat can act as an optical turning film or element for use in an opticaldisplay.

The base layer can be of a nature and composition suitable for use in anoptical product, i.e. a product designed to control the flow of light.Almost any material can be used as a base material as long as thematerial is sufficiently optically clear and is structurally strongenough to be assembled into or used within a particular optical product.A base material can be chosen that has sufficient resistance totemperature and aging that performance of the optical product is notcompromised over time.

Useful base materials include, for example, styrene-acrylonitrile,cellulose acetate butyrate, cellulose acetate propionate, cellulosetriacetate, polyether sulfone, polymethyl methacrylate, polyurethane,polyester, polycarbonate, polyvinyl chloride, polystyrene, polyethylenenaphthalate, copolymers or blends based on naphthalene dicarboxylicacids, polycyclo-olefins, polyimides, and glass. Optionally, the basematerial can contain mixtures or combinations of these materials. In anembodiment, the base may be multi-layered or may contain a dispersedcomponent suspended or dispersed in a continuous phase.

For some optical products such as microstructure-bearing products suchas, for example, brightness enhancement films, examples of preferredbase materials include polyethylene terephthalate (PET) andpolycarbonate. Examples of useful PET films include photogradepolyethylene terephthalate and MELINEX™ PET available from DuPont Filmsof Wilmington, Del.

Some base materials can be optically active, and can act as polarizingmaterials. A number of bases, also referred to herein as films orsubstrates, are known in the optical product art to be useful aspolarizing materials. Polarization of light through a film can beaccomplished, for example, by the inclusion of dichroic polarizers in afilm material that selectively absorbs passing light. Light polarizationcan also be achieved by including inorganic materials such as alignedmica chips or by a discontinuous phase dispersed within a continuousfilm, such as droplets of light modulating liquid crystals dispersedwithin a continuous film. As an alternative, a film can be prepared frommicrofine layers of different materials. The polarizing materials withinthe film can be aligned into a polarizing orientation, for example, byemploying methods such as stretching the film, applying electric ormagnetic fields, and coating techniques.

Examples of polarizing films include those described in U.S. Pat. Nos.5,825,543 and 5,783,120. The use of these polarizer films in combinationwith a brightness enhancement film has been described in U.S. Pat. No.6,111,696.

A second example of a polarizing film that can be used as a base arethose films described in U.S. Pat. No. 5,882,774. Films availablecommercially are the multilayer films sold under the trade designationDBEF (Dual Brightness Enhancement Film) from 3M. The use of suchmultilayer polarizing optical film in a brightness enhancement film hasbeen described in U.S. Pat. No. 5,828,488.

A common way of measuring the effectiveness of such recycling of lightis to measure the gain of an optical film. As used herein, “relativegain”, is defined as the on-axis luminance, as measured by the testmethod described in the examples, when an optical film (or optical filmassembly) is placed on top of the light box, relative to the on-axisluminance measured when no optical film is present on top of the lightbox. This definition can be summarized by the following relationship:

Relative Gain=(Luminance measured with optical film)/(Luminance measuredwithout optical film)

In one embodiment, an optical film comprising a light transmissive (e.g.cured) polymeric material having a microstructured surface is described.The optical film is a substantially non-polarizing film having a singlesheet relative gain of at least 1.60. The relative single sheet gain istypically no greater than 2.05. Accordingly, the single sheet relativegain may also range from any values in the set of relative gain valuesincluding 1.65, 1.70, 1.75, 1.80, 1.85, and 1.90 or greater.

In other embodiments, the inventions relate to various assemblies thatcomprise or consist of two or more films. Each assembly includes a firstmicrostructured optical film proximate a second (e.g. microstructured orunstructured) optical film.

By proximate, it is meant sufficiently near. Proximate can include thefirst microstructured optical film being in contact with the secondoptical film such as by the films merely being stacked together or thefilms may be attached by various means. The films may be attached bymechanical means, chemical means, thermal means, or a combinationthereof. Chemical means includes various pressure sensitive,solvent-based, and hot melt adhesives as well as two-part curableadhesive compositions that crosslink upon exposure to heat, moisture, orradiation. Thermal means includes for example a heated embossed roller,radio frequency (RF) welding, and ultrasonic welding. The optical filmsmay be attached (e.g. continuously) across the entire plane of thefilms, at only select points, or at only the edges. Alternatively, theproximate optical films may be separated from each other with an airinterface. The air interface may be created by increasing the thicknessof either or both optical films at the periphery, such as by applicationof an adhesive. When the films are stacked rather than laminatedtogether, the air interface between the optical films may be only a fewmicrons.

In some embodiments, a first microstructured optical film is proximate asecond microstructured optical film. In such assemblies, themicrostructured surface of the bottom film is preferably disposedproximate the unstructured surface of the top film. For embodiments thatemploy prismatic microstructured films, the prisms of the films aregenerally aligned parallel in one principal direction, the prisms beingseparated by grooves. It is generally preferred to align the prisms (orgrooves) of the second (e.g. bottom) microstructured optical film in astack such that the prisms are substantially orthogonal to the prisms ofthe first (e.g. top) film. However, other alignments can also beemployed. For example, the prisms of the second optical film may bepositioned relative to the prisms of the second optical film such thatthe intersection of grooves or prisms form angles ranging from about 70°to about 120°.

In one embodied assembly, a first microstructured substantiallynon-polarizing optical film is proximate a second microstructuredsubstantially non-polarizing optical film. The gain of this assembly isat least 2.50. The first optical film may be the same as or differentthan the second optical film. For example, the second film may have adifferent base layer composition, a different microstructured surfacecomposition, and/or may have a different surface microstructure. Therelative gain of this assembly is typically less than 3.32. Accordingly,the relative gain of such assembly may also range from any values in theset of relative gain values including 2.55, 2.60, 2.65, 2.70, 2.75,2.80, 2.85, 2.90, 2.95, and 3.00 or greater.

For the following defined terms, these definitions shall be applied,unless a different definition is given in the claims or elsewhere inthis specification.

The term “microstructure” is used herein as defined and explained inU.S. Pat. No. 4,576,850. Thus, it means the configuration of a surfacethat depicts or characterizes the predetermined desired utilitarianpurpose or function of the article having the microstructure.Discontinuities such as projections and indentations in the surface ofsaid article will deviate in profile from the average center line drawnthrough the microstructure such that the sum of the areas embraced bythe surface profile above the center line is equal to the sum of theareas below the line, said line being essentially parallel to thenominal surface (bearing the microstructure) of the article. The heightsof said deviations will typically be about +/−0.005 to +/−750 microns,as measured by an optical or electron microscope, through arepresentative characteristic length of the surface, e.g., 1-30 cm. Saidaverage center line can be piano, concave, convex, aspheric orcombinations thereof. Articles where said deviations are of low order,e.g., from +/−0.005+/−0.1 or, preferably, +/−0.05 microns, and saiddeviations are of infrequent or minimal occurrence, i.e., the surface isfree of any significant discontinuities, are those where themicrostructure-bearing surface is an essentially “flat” or “smooth”surface, such articles being useful, for example, as precision opticalelements or elements with a precision optical interface, such asophthalmic lenses. Articles where said deviations are of low order andof frequent occurrence include those having anti-reflectivemicrostructure. Articles where said deviations are of high-order, e.g.,from +/−0.1 to +/−750 microns, and attributable to microstructurecomprising a plurality of utilitarian discontinuities which are the sameor different and spaced apart or contiguous in a random or orderedmanner, are articles such as retroreflective cube-corner sheeting,linear Fresnel lenses, video discs and brightness enhancing films. Themicrostructure-bearing surface can contain utilitarian discontinuitiesof both said low and high orders. The microstructure-bearing surface maycontain extraneous or non-utilitarian discontinuities so long as theamounts or types thereof do not significantly interfere with oradversely affect the predetermined desired utilities of said articles.

“Index of refraction,” or “refractive index,” refers to the absoluterefractive index of a material (e.g., a monomer) that is understood tobe the ratio of the speed of electromagnetic radiation in free space tothe speed of the radiation in that material. The refractive index can bemeasured using known methods and is generally measured using an Abberefractometer or Bausch and Lomb Refractometer (CAT No. 33.46.10) in thevisible light region (available commercially, for example, from FisherInstruments of Pittsburgh, Pa.). It is generally appreciated that themeasured index of refraction can vary to some extent depending on theinstrument.“(Meth)acrylate” refers to both acrylate and methacrylate compounds.The term “nanoparticles” is defined herein to mean particles (primaryparticles or associated primary particles) with a diameter less thanabout 100 nm.“Surface modified colloidal nanoparticle” refers to nanoparticles eachwith a modified surface such that the nanoparticles provide a stabledispersion.“Stable dispersion” is defined herein as a dispersion in which thecolloidal nanoparticles do not agglomerate after standing for a periodof time, such as about 24 hours, under ambient conditions—e.g. roomtemperature (about 20-22° C.), atmospheric pressure, and no extremeelectromagnetic forces.“Aggregation” refers to a strong association between primary particlesthat may be chemically bound to one another. The breakdown of aggregatesinto smaller particles is difficult to achieve.“Agglomeration refers to a weak association between primary particleswhich may be held together by charge or polarity and can be broken downinto smaller entities.“Primary particle size” refers to the mean diameter of a single(non-aggregate, non-agglomerate) particle.The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5).As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” include plural referents unless the contentclearly dictates otherwise. Thus, for example, reference to acomposition containing “a compound” includes a mixture of two or morecompounds. As used in this specification and the appended claims, theterm “or” is generally employed in its sense including “and/or” unlessthe content clearly dictates otherwise.Unless otherwise indicated, all numbers expressing quantities ofingredients, measurement of properties and so forth used in thespecification and claims are to be understood as being modified in allinstances by the term “about.”The present invention should not be considered limited to the particularexamples described herein, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention can be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the instant specification.

EXAMPLES 1. Synthesis of Acrylic acid4-[1,1-bis-(4-acryloyloxy-phenyl)-ethyl]-phenyl ester

A 500 ml round bottom flask is equipped with a mechanical stirrer,thermometer and addition funnel. Add 50 grams1,1,1-tris(4-hydroxyphenyl) ethane, 180 grams DMF and 57.8 grams oftriethylamine. Stir well at room temperature. Add 48.7 grams of acryloylchloride dropwise to this mixture, keeping the pot temperature at 25-30°C. After completing the addition, stir the mixture for one hour at 25°C. Add 200 g. ethyl acetate and wash the organic portion four times with150 g. water and then with 150 g. water/20 g. HCl, then with 150 g.saturated brine. Strip the solvent from the mix on a rotary evaporator.

Pass the crude mixture through a large silica gel column, using 20%ethyl acetate/80% hexanes as the elutant. Collect the appropriateproduct fractions and strip the solvent. Obtain 5 grams of an off-whitesolid. The mp is 130° C. and a refractive index of at least 1.55.

2. Synthesis of2-(4-{1,1-bis-[4-(2-hydroxy-ethoxy)-phenyl]-ethyl}-phenoxy)-ethanolIntermediate

A 500 ml round bottom flask is equipped with a mechanical stirrer,thermometer and condenser. Add 50 grams 1,1,1-tris(4-hydroxyphenyl)ethane, 100 grams DMF, 0.5 g. potassium iodide and 47.4 grams ofethylene carbonate. Heat to 145° C. and hold for 6 hours. Add 200 g.ethyl acetate and wash the organic portion four times with 150 g.saturated brine. Strip the solvent from the mix on a rotary evaporator.The yield of tan solid is 78 grams. Recrystallize this crude product bydissolving in 300 g. boiling ethyl acetate and allowing to cool slowly.Collect 70.3 grams of a tan solid; the mp=78-81° C.

Synthesis of Acrylic acid2-(4-{1,1-bis-[4-(2-acryloyloxy-ethoxy)-phenyl]-ethyl}-phenoxy)-ethylester (“TTA-1”)

A 1000 ml round bottom flask is equipped with a mechanical stirrer,thermometer and dean-stark trap with condenser. Add 50 grams2-(4-{1,1-Bis-[4-(2-hydroxy-ethoxy)-phenyl]-ethyl}-phenoxy)-ethanol, 400grams toluene, 2 g. para-toluene sulfonic acid (PTSA), 27.1 gramsacrylic acid and 0.04 grams of hindered amine nitroxide inhibitorcommercially available from Ciba Specialty Chemical, Inc. Tarrytown,N.Y. under the trade designation “Prostab 5198”. Heat to reflux and holdfor 6 hours. Cool to room temperature, then add 0.7 grams PTSA and 7grams acrylic acid. Heat to reflux and hold for five hours. Wash theorganic portion with 250 g. water with 25 g sodium carbonate, then twicewith 250 g. saturated brine. Strip the solvent from the mix on a rotaryevaporator. The crude product is dissolved in 500 g ethyl acetate andpassed through a short bed of silica gel with ethyl acetate as theelutant. Remove the solvent on a rotary evaporator to give 50 grams of alight yellow oil. The refractive index is 1.554.

3. Synthesis of 2,6-Diphenylphenoxyethanol Intermediate

To a 50 ml 1 neck round bottom was added 2,6-diphenylphenol (10 g, 1eq), ethylene carbonate (3.9 g, 1.1 eq), potassium iodide (0.07 g, 0.01eq), dimethylformamide (1 g, 0.3 eq) and heated to 150 C. After 4 hoursthe reaction was cooled to 40 C, added 30 ml ethyl acetate and washed 2times with 20 ml sodium chloride brine, 3 times with 20 ml DI water andagain with 20 ml brine. The ethyl acetate was dried with (1 g) magnesiumsulfate, filtered and concentrated invacuo to recover an off-whitesolid. Mp 77-78

Synthesis of 2,6-Diphenylphenoxyethyl acrylate (“TPA-1”)

To a 50 ml 1 neck round bottom equipped with a dean stark trap was added2,6-diphenylphenoxyethanol (5 g, 1 eq), toluene (21 ml), acrylic acid(2.7 g, 2.2 eq), methane sulfonic acid (0.3 g, 0.18 eq), Prostab 5198(0.003 g) and heated to reflux. After 3 hours the reaction was complete.The reaction was washed with 20 ml sodium carbonate and 20 ml sodiumchloride brine. The toluene mixture was filtered through thin layer ofsilica gel and eluted with 30 ml toluene. The filtrate was treated withthe “Prostab 5198” (0.003 g) and concentrated invacuo to recover aviscous oil. >97% by GC. RI=1.6062 at 25° C.

Polymerizable Resin Composition 1:

65 parts CN120 (epoxy acrylate available from Sartomer Company, Exton,Pa., reported by Sartomer to have a viscosity of 2150 cps at 65° C., arefractive index of 1.5556 and a Tg of 60° C.), 15 parts SR339(2-phenoxyethyl acrylate available from Sartomer Company, Exton, Pa.,reported by Sartomer to have a viscosity of 12 cps at 25° C., arefractive index of 1.516 and a Tg of 5° C.), 20 parts TTA-1 (with arefractive index of 1.554), and 0.3 parts Darocur 4265 (available fromCiba Specialty Chemicals, Tarrytown, N.Y.) were mixed togetherthoroughly in an amber jar.

Polymerizable Resin Composition 2:

50 parts CN120, 50 parts TTA-1 (with a refractive index of 1.554), and0.3 parts Darocur 4265 (available from Ciba Specialty Chemicals,Tarrytown, N.Y.) were mixed together thoroughly in an amber jar.

Polymerizable Resin Composition 3:

100 parts TTA-1 (with a refractive index of 1.554), and 0.3 partsDarocur 4265 (available from Ciba Specialty Chemicals, Tarrytown, N.Y.)were mixed together thoroughly in an amber jar.

Polymerizable Resin Composition 4:

30 parts of TPA-1 (with a refractive index of 1.606), 35 parts CN120, 35parts SR601 (ethoxylated bisphenol A diacrylate available from SartomerCompany reported to have a viscosity of 1080 cps at 25° C., a refractiveindex of 1.5340 and a Tg of 60° C.) and 0.3 parts Darocur 4265(available from Ciba Specialty Chemicals, Tarrytown, N.Y.) were mixedtogether thoroughly in an amber jar.

Optical Film Sample Preparation:

Brightness enhancing films samples were made using Polymerizable ResinCompositions 1 and 2. About 3 grams of warm resin was applied to a 2 milprimed PET (polyester) film, available from DuPont under the tradedesignation “Melinex 623” and placed against a microstructured tool witha 90/24 pattern similar to the commercially available VikuitiTBEF-90/24. The PET, resin and tool were passed through a heatedlaminator set at approximately 150° F. to create a uniformly thicksample. The tool containing the film and coated resin sample was passedat 30 fpm through a Fusion UV processor containing two 600 W/in D-bulbs.The PET and cured resin were removed from the tool and cut into samples.

Gain Test Method

Optical performance of the films was measured using a SpectraScan™PR-650 SpectraColorimeter with an MS-75 lens, available from PhotoResearch, Inc, Chatsworth, Calif. The films were placed on top of adiffusely transmissive hollow light box. The diffuse transmission andreflection of the light box can be described as Lambertian. The lightbox was a six-sided hollow cube measuring approximately 12.5 cm×12.5cm×11.5 cm (L×W×H) made from diffuse PTFE plates of ˜6 mm thickness. Oneface of the box is chosen as the sample surface. The hollow light boxhad a diffuse reflectance of ˜0.83 measured at the sample surface (e.g.˜83%, averaged over the 400-700 nm wavelength range, measurement methoddescribed below). During the gain test, the box is illuminated fromwithin through a ˜1 cm circular hole in the bottom of the box (oppositethe sample surface, with the light directed towards the sample surfacefrom the inside). This illumination is provided using a stabilizedbroadband incandescent light source attached to a fiber-optic bundleused to direct the light (Fostec DCR-II with ˜1 cm diameter fiber bundleextension from Schott-Fostec LLC, Marlborough MA and Auburn, N.Y.). Astandard linear absorbing polarizer (such as Melles Griot 03 FPG 007) isplaced between the sample box and the camera. The camera is focused onthe sample surface of the light box at a distance of ˜34 cm and theabsorbing polarizer is placed ˜2.5 cm from the camera lens. Theluminance of the illuminated light box, measured with the polarizer inplace and no sample films, was >150 cd/m². The sample luminance ismeasured with the PR-650 at normal incidence to the plane of the boxsample surface when the sample films are placed parallel to the boxsample surface, the sample films being in general contact with the box.The relative gain is calculated by comparing this sample luminance tothe luminance measured in the same manner from the light box alone. Theentire measurement was carried out in a black enclosure to eliminatestray light sources.

The diffuse reflectance of the light box was measured using a 15.25 cm(6 inch) diameter Spectralon-coated integrating sphere, a stabilizedbroadband halogen light source, and a power supply for the light sourceall supplied by Labsphere (Sutton, N.H.). The integrating sphere hadthree opening ports, one port for the input light (of 2.5 cm diameter),one at 90 degrees along a second axis as the detector port (of 2.5 cmdiameter), and the third at 90 degrees along a third axis (i.e.orthogonal to the first two axes) as the sample port (of 5 cm diameter).A PR-650 Spectracolorimeter (same as above) was focused on the detectorport at a distance of ˜38 cm. The reflective efficiency of theintegrating sphere was calculated using a calibrated reflectancestandard from Labsphere having ˜99% diffuse reflectance (SRT-99-050).The standard was calibrated by Labsphere and traceable to a NISTstandard (SRS-99-020-REFL-51). The reflective efficiency of theintegrating sphere was calculated as follows:

Sphere brightness ratio=1/(1−Rsphere*Rstandard)

The sphere brightness ratio in this case is the ratio of the luminancemeasured at the detector port with the reference sample covering thesample port divided by the luminance measured at the detector port withno sample covering the sample port. Knowing this brightness ratio andthe reflectance of the calibrated standard (Rstandard), the reflectiveefficiency of the integrating sphere, Rsphere, can be calculated. Thisvalue is then used again in a similar equation to measure a sample'sreflectance, in this case the PTFE light box:

Sphere brightness ratio=1/(1−Rsphere*Rsample)

Here the sphere brightness ratio is measured as the ratio of theluminance at the detector with the sample at the sample port divided bythe luminance measured without the sample. Since Rsphere is known fromabove, Rsample can be calculated. These reflectances were calculated at4 nm wavelength intervals and reported as averages over the 400-700 nmwavelength range.The single sheet gain is tested in the vertical (or perpendicularorientation relative to the front face of the diffuser boxed used in theE.T. Tester). In the horizontal, or crossed sheet configuration, thebottom sheet of the film stack is in the vertical orientation and thetop sheet is horizontal or parallel to the front face of the diffuserbox.Table 1 as follows depicts the test results of the optical filmsprepared from Polymerizable Resin Compositions 1 and 2.

TABLE 1 Polymerizable Resin Composition Single Sheet Gain Crossed SheetGain 1 1.61 2.54 2 1.62 2.57 3 1.61 2.50 4 1.64 2.61

What is claimed is:
 1. An optical film comprising a polymerizedmicrostructured surface wherein the polymerized microstructured surfacecomprises the reaction product of a polymerizable resin compositioncomprising at least one triphenyl monomer having the general structure

wherein R2 is independently H or a substituent comprising a(meth)acrylate group and at least two R2 substituents comprise a(meth)acrylate group; X is independently halogen, aryl, hydroxyl, or aC₁ to C₁₂ alkyl group; R3 is independently hydrogen, aryl, or a C₁ toC₁₂ alkyl group; and p is 0 to
 5. 2. The optical film of claim 1 whereinp is
 0. 3. The optical film of claim 1 wherein R2 is independently a(meth)acrylate substitutent selected from

wherein Q is O or S; L is a C₂ to C₆ alkylene group optionallysubstituted with a one or more hydroxyl groups; n ranges from 0 to 10;R1 is H or CH₃; and R3 is hydrogen, aryl, or a C₁ to C₁₂ alkyl group. 4.The optical film of claim 3 wherein Q is O.
 5. The optical film of claim3 wherein L is C₂ or C₃ and n is
 1. 6. The optical film of claim 1wherein the triphenyl monomer is a di(meth)acrylate.
 7. The optical filmof to claim 1 wherein the triphenyl monomer is a tri(meth)acrylate. 8.The optical film of claim 1 wherein the polymerizable resin compositioncomprises up to 50 wt-% of one or more triphenyl (meth)acrylatemonomers; and 25 wt-% to 75 wt-% of one or more multi(meth)acrylatemonomers or oligomers having at least two polymerizable (meth)acrylategroups.
 9. The optical film of claim 1 wherein the multi(meth)acrylatemonomer comprises one or more bisphenol A (meth)acrylates, aromaticepoxy (meth)acrylates, and mixtures thereof.
 10. The optical film ofclaim 1 wherein the polymerizable resin composition comprises less than1 wt-% total of chlorine, bromine, or mixtures thereof.
 11. The opticalfilm of claim 1 wherein the polymerizable resin composition comprisesless than 1 wt-% total of chlorine, bromine, fluorine and iodine. 12.The optical film of claim 1 wherein the polymerizable resin is free ofinorganic nanoparticles.
 13. The optical film of claim 1 wherein thepolymerizable resin comprises at least 10 wt-% of surface modifiedinorganic nanoparticles.
 14. The optical film of claim 13 wherein theinorganic nanoparticles have a refractive index of at least 1.68. 15.The optical film of claim 14 wherein the inorganic nanoparticlescomprise zirconia.
 16. The optical film of claim 1 wherein the opticalfilm is a brightness enhancing film having a single sheet gain of atleast 1.59.